This invention relates to an intake device for an engine used in a motorcycle and other powered small vehicles, such as snowmobiles, and tricycles. In the conventional engine device of this type, a first air/fuel intake valve is located at the downstream end of the first intake passage that is connected to the primary carburetor. A second air/fuel intake valve is located at the downstream end of the second intake passage that is connected to the secondary carburetor. By connecting both air/fuel intake passages to each other through a pathway situated in the middle of said intake passages, when the secondary carburetor does not function, in order to improve combustion, a part of fresh air in the first intake passage is led from said primary carburetor to said secondary carburetor through said pathway to dilute residual gas in the second intake passway. Such a system has been proposed. However, in such a device, the air/fuel mixture is liable to be led to the first intake passage through the pathway at the time of its backflow. This would degrade rather than assist in engine performance during a partial malfunction.